Reciprocating internal combustion engines typically include a cast iron or aluminum engine block having at least one cylindrical bore formed therein that defines a cylinder in which a reciprocating piston is received. An open-ended ring known as a piston ring is typically positioned within an annular groove formed in an outer circumference of the piston. The intrinsic spring force of the piston ring ensures sufficient contact between the piston ring and an inner wall of the cylinder. During engine operation, the piston moves up and down within the cylinder and the pressure exerted on the cylinder wall by the piston ring produces a seal between the piston and the inner wall of the cylinder. This seal helps prevent escape of combustion gases from the combustion chamber and may help control oil consumption. Piston rings also may help transfer heat away from the piston to the cylinder wall. A cylinder sleeve or liner may be received within the cylindrical bore of the engine block to provide the cylinder with improved thermal characteristics and a compatible wear surface along which the piston can slide.
Thermal gradients may occur within piston rings and cylinder liners during normal engine operation due to the inherent temperature difference between the pistons and the inner walls of the cylinders. For example, in a diesel internal combustion engine, the pistons may operate at temperatures of about 300° C. and the cylinder walls may operate at temperatures of about 115° C. In a piston ring of a reciprocating internal combustion engine, a thermal gradient may occur between an outer portion of the piston ring that is in contact with the relatively cool cylinder wall and an inner portion of the piston ring that is in contact with or in close proximity to the relatively hot piston. In such case, if the inner and outer portions of the piston ring are made of the same material, the inner portion of the piston ring may experience a greater degree of thermal expansion than the outer portion of the piston ring, which may result in an uneven distribution of the radial contact pressure between the piston ring and the cylinder wall. In particular, the generation of a radial thermal gradient within a split piston ring having free ends may result in an increased amount of radial contact pressure between the free ends of the piston ring and the cylinder wall, which may increase the amount of wear at the free ends of the piston ring and also may lead to scuffing of the cylinder wall. In a cylinder liner, a thermal gradient may occur between an outer portion of the liner that is in contact with the relatively cool engine block and an inner portion of the liner that is in contact with or in close proximity to the relatively hot piston.